...when you update to 1.2-RC3 and higher. In fact Michel Salim found out that Liferea uses the wrong GNOME font definition. For starters: in the GNOME preferences you can configure fonts for different use cases: application font, document font, desktop font, window title font and monospace font. Until now Liferea did use the application font instead of the document font.
With the patch from Michel Salim the problem is corrected now and Liferea should use the same font other applications use to present document content to you. So when you start up Liferea after upgrading to 1.2-RC3 it will look much better :-)